The present invention relates to the field of fuses and fuse structures. More particularly, the invention is directed to a sub-miniature fuse having a high current capacity.
Miniature and sub-miniature fuses are very popular due to the small space they occupy. A conventional sub-miniature fuse has a cylindrical housing of approximately 6 mm in height and approximately 8 mm in outer diameter. The switching, or fusing, capacity of these fuses is usually on the order of 35 amps under 250 volts or 100 amps under 125 volts. In numerous applications, an even higher switching capacity is necessary. Thus, early arc quenching within the fuse is required. An arc is created after the melting of the fusible conductor has started and allows the current to continue to flow in spite of the separation of the fusible conductor or wire in response to an over-current condition. Due to the continued arcing, the pressure and temperature within the fuse housing will rise because of the continued addition of energy. The buildup in pressure may continue until the maximum load pressure of the fuse is exceeded and the fuse housing is destroyed. Thus, the fuse explodes. In order to prevent such a marked rise in pressure and temperature within the fuse housing, the fuse chamber is filled with an energy-absorbing mass. For instance, a metal is used as an energy-absorbing mass in German Pat. No. 724,865. Other attempts in the prior art have been made to relieve the critical buildup of pressure in a fuse by using a metal cap which is soldered or welded onto a base of ceramic material. Fuses of this type are disclosed in German utility model No. 85 07 615.5.
The prior art attempts to overcome the pressure buildup in fuses have lead to no significant improvement or reduction of the problem. Thus, conventional fuses remain deficient in this regard.